Analysis of tetrapyrrolic pigments and derivatives in sediments by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A new application is described of the on-line high-performance liquid chromatography/positive and negative ion atmospheric pressure chemical ionization mass spectrometry (APCI(+/–)-MS) to the identification of tetrapyrrolic compounds in sediment samples containing complex mixtures of natural pigments and their diagenetic products. The method relies on the production of radical anions in order to determine the molecular masses of the molecules which yield abundant fragment ions when analyzed in the positive mode. This approach allows to verify the occurrence of coeluting components by examining their negative ion spectra and to complete their identification on the basis of their fragment ions produced in the positive ion spectra. Received: 24 September 1998 / Revised: 23 December 1998 / Accepted: 29 December 1998     

Fiber Optic Ion-Microsensors Based on Luminescence Lifetime

 Fiber optic ion-microsensors based on luminescence decay time have been developed for chloride and potassium. The fiber tip coatings consist of the respective ion-selective lipophilic ion carrier, plasticized PVC, and the ruthenium(II) tris-4,4′-diphenyl-2,2′-bipyridyl ion-pair with Bromothymol Blue [Ru(dibipy)₃(BTB)₂] as a proton donor. The efficacy of radiationless fluorescence energy transfer from the donor (the ruthenium complex) to the acceptor (BTB) is mediated by the ion concentration within the samples. The chloride response is based on the co-extraction of chloride along with protons from the aqueous sample into a plastiziced PVC membrane, whereas in the presence of potassium ions in the sample, the neutral BTB becomes deprotonated on extraction of potassium ions, with the release of protons. Both processes result in a change in BTB absorbance. The absorption band of deprotonated BTB overlaps significantly with the emission band of the ruthenium complex, allowing radiationless energy transfer to take place. Received July 8, 1998. Revision November 10, 1998.     

Analysis of tetrapyrrolic pigments and derivatives in sediments by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A new application is described of the on-line high-performance liquid chromatography/positive and negative ion atmospheric pressure chemical ionization mass spectrometry (APCI(+/–)-MS) to the identification of tetrapyrrolic compounds in sediment samples containing complex mixtures of natural pigments and their diagenetic products. The method relies on the production of radical anions in order to determine the molecular masses of the molecules which yield abundant fragment ions when analyzed in the positive mode. This approach allows to verify the occurrence of coeluting components by examining their negative ion spectra and to complete their identification on the basis of their fragment ions produced in the positive ion spectra. Received: 24 September 1998 / Revised: 23 December 1998 / Accepted: 29 December 1998     

Quasi-monocrystalline silicon for thin-film devices

Thermal crystallization of a double layer porous Si film creates a monocrystalline Si film with a thin separation layer between the Si film and the reusable starting wafer. The process enables transfer of thin monocrystalline Si films to foreign substrates, whereby devices may be formed before or after separation of the film. Sub-micrometer thick films are almost compact, while films with a thickness of several μm contain voids, and are therefore termed “quasi-monocrystalline”. Internal voids strongly enhance optical absorption by light scattering. The hole mobility is 78 cm² V^-1 s^-1 at a p-type starting wafer resistivity of 0.05 Ω cm. Received: 24 March 1999 / Accepted: 29 March 1999 / Published online: 5 May 1999     

Comparison of polyelectrolyte multilayers built up with polydiallyldimethylammonium chloride and poly(ethyleneimine) from salt-free solutions by in-situ surface plasmon resonance measurements

Polyelectrolytes offer a widespread potential for the defined modification of planar inorganic or polymer surfaces. Essential parameters for the regular adsorption of subsequent polymer layers by electrostatic interactions are the charge of polyelectrolyte and of the outermost surface region, the surface of the substrate, and the molar mass of the polyelectrolyte. To study such effects in mono- and multilayers we used poly(diallyldimethylammonium chloride (PD) with a molar mass from 5000 to 400000 g/mol as a strong polycation and poly(ethyleneimine) (PEI) with 75000 g/mol as a weak polycation and poly(sodium styrenesulfonate) (PSS) from 70000 to 1Mio g/mol in the diluted and semi-diluted region. The characterization of the layers was performed by streaming potential, in-situ SPR and UV-Vis spectroscopy. Thereby the layer built up at the solid/liquid-interface could be followed and quantified at the molecular level. SPR revealed that the thicknesses of the multilayer depends strongly on pK values of the polyelectrolyte (strong or weak) and the molar masses. We observed a linear growth if both polyelectrolytes are strong and an exponential growth if one polyelectrolyte is weak. The thickness increased with higher molar masses of the polyelectrolytes. The process was followed in-situ in short time steps.     

Sensitivity Analysis of Human Leg Metabolical Costs

The human walking is characterized by skeletal dynamics and muscle excitation patterns minimizing the metabolical energy. This criterion is applied to assess the performance of lower limb prosthetic devices, and to evaluate therapies for patients presenting gait disorders. It is desirable, therefore, to dispose models of the human normal and pathological gaits capable of estimating the metabolical energy expenditure. For the swing phase of normal and pathological gaits a musculoskeletal model of the lower limb is presented to estimate metabolical energy expenditure. The mechanical model has three degrees of freedom and is actuated by eight Hill-type muscle units, and the model for the metabolical costs is adopted from literature. In this paper a combination of inverse and direct dynamics is used, and a sensitivity analysis of the dynamical behavior and the corresponding metabolical costs estimations with respect to parametrized neural excitations is performed. The leg motions are based on experiments in a gait analysis laboratory. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multi-Band Gutzwiller Wave Functions for Itinerant Ferromagnetism

Multi-band Gutzwiller-correlated wave functions reconcile the contrasting concepts of itinerant band electrons versus electrons localized in partially filled atomic shells. The approximate evaluation of these variational ground states becomes exact in the limit of large coordination number. The result allows the identification of quasi-particle band structures for correlated electron systems. As a first application, we summarize a study of itinerant ferromagnetism in a two-band model, thereby elucidating the co-operation of the Coulomb repulsion and the Hund's-rule exchange. Then, we present results of calculations for ferromagnetic nickel, using a realistic 18 spin-orbital basis of 4s, 4p and 3d valence electrons. Good agreement with the experimental ground-state properties of nickel is obtained. In particular, the quasi-particle energy bands agree much better with the photo-emission and Fermi surface data than the band structure obtained from spin-density functional theory. Finally, we present results for the variational spinwave dispersion for our two-band model.     

Thermodynamic modeling of Fe–Ni pentlandite

Gibbs energy modeling of iron–nickel pentlandite has been performed using experimental data of ternary phase equilibria. A three-sublattice approach in the framework of the Compound Energy Formalism is developed to refine a two-sublattice model of pentlandite recently applied within a complete assessment of the Fe–Ni–S system. Experimental data about the iron site fraction on the octahedral sublattice at 523.15 K for the composition Fe₅Ni₄S₈ as well as the enthalpy of formation at 298.15 K for the composition Fe_4.5Ni_4.5S₈ are predicted satisfactorily by the novel model. New possibilities to interpret experimental phase equilibrium data on complex phase relations with pentlandite are discussed together on the basis of the recent extension of a second high-temperature heazlewoodite phase to a ternary solution phase.     

Chemical Analysis and In Vitro Bioactivity of Essential Oil of Laurelia sempervirens and Safrole Derivatives against Oomycete Fish Pathogens

In this study, the essential oil (EO) from Laurelia sempervirens was analyzed by GC/MS and safrole (1) was identified as the major metabolite 1, was subjected to direct reactions on the oxygenated groups in the aromatic ring and in the side chain, and eight compounds (4 to 12) were obtained by the process. EO and compounds 4–12 were subjected to biological assays on 24 strains of the genus Saprolegnia, specifically of the species 12 S. parasitica and 12 S. australis. EO showed a significant effect against Saprolegnia strains. Compound 6 presents the highest activity against two resistant strains, with minimum inhibitory concentration (MIC) and minimum oomyceticidal concentration (MOC) values of 25 to 100 and 75 to 125 µg/mL, respectively. The results show that compound 6 exhibited superior activities compared to the commercial controls bronopol and azoxystrobin used to combat these pathogens.     

Brownmillerites CaFeO2.5 and SrFeO2.5 as Catalyst Support for CO Oxidation

The support material can play an important role in oxidation catalysis, notably for CO oxidation. Here, we study two materials of the Brownmillerite family, CaFeO_2.5 and SrFeO_2.5, as one example of a stoichiometric phase (CaFeO_2.5, CFO) and one existing in different modifications (SrFeO_2.75, SrFeO_2.875 and SrFeO₃, SFO). The two materials are synthesized using two synthesis methods, one bottom-up approach via a complexation route and one top-down method (electric arc fusion), allowing to study the impact of the specific surface area on the oxygen mobility and catalytic performance. CO oxidation on ¹⁸O-exchanged materials shows that oxygen from SFO participates in the reaction as soon as the reaction starts, while for CFO, this onset takes place 185 °C after reaction onset. This indicates that the structure of the support material has an impact on the catalytic performance. We report here on significant differences in the catalytic activity linked to long-term stability of CFO and SFO, which is an important parameter not only for possible applications, but equally to better understand the mechanism of the catalytic activity itself.